RFR: JDK-8074579 Use more efficient and readable way of checking PKZIP signatures

[Xueming Shen]

The result looks good, though I doubt it will bring in any real "meaningful" performance
improvement when reading a zip/jar file. But faster is faster. The same improvement might
not applied to the java version, given those range check?

-Sherman

On 03/09/2015 01:14 PM, Martin Buchholz wrote:
> I actually benchmarked my last suggestion to be 20% faster on an ad-hoc microbenchmark.  We can go faster yet on x86 if we use unaligned 4-byte uint32 reads.  Maybe in a future change.
>
> In general, hardware is moving in the direction of allowing unaligned reads without performance penalty, especially on x86, and it would be good to start taking advantage of that.
>
> On Fri, Mar 6, 2015 at 9:50 PM, Martin Buchholz <martinrb at google.com <mailto:martinrb at google.com>> wrote:
>
>     Err...
>
>     #define PKZIP_SIGNATURE_AT(p, b2, b3) \
>       (((p)[0] == 'P') & ((p)[1] == 'K') & ((p)[2] == b2) & ((p)[3] == b3))
>
>